Ultrahigh-frequency oscillation generator



April 22, 1952 J; H. FREMLIN ET AL ULTRAHIGH-FREQUENCYOSCILLATIONGENERATOR 3 Sheets-Sheet 1 Filed Sept. 9, 1942 J. H. FREMLINET AL ULTRAHIGH- Filed Sept. 9, 1942 April 22, 1952 FREQUENCYOSCILLATION GENERATOR 3 Sheets-Sheet B JO/mfis/M W Mm A tlorney April22, 1952 J. H. FREMLIN ET AL 2,593,433

ULTRAHIGH-FREQUENCY OSCILLATION GENERATOR Filed S t 9; 1942 5Sheets-Shae: 5

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Attorney Patented Apr. 22, 1952 ULTRAHIGH-FREQUENCY OSCILLATIONGENERATOR John Heaver Fremlin and John Foster, London, England,assignors, by mesne assignments, to International Standard ElectricCorporation, New York, N. Y., a corporation of Delaware ApplicationSeptember 9, 1942, Serial No. 457,789 In Great Britain September 19,1941 12 Claims.

The present invention relates to electron discharge devices, andparticularly to ultra high frequency oscillators, of the velocitymodulation type. Such devices may comprise one or more resonant cavitiesor chambers bounded by conducting walls, each provided with a gapleading to the chamber, an electron stream being directed past said gapor gaps in succession so that either the electrons are velocitymodulated by the electric field across the gap or energy is abstractedby the field from the velocity modulated electrons passing the gap. Atthe first gap the electrons are velocity modulated by the electric fieldacross this gap, then they traverse the distance between the two gapsduring which they are shielded from the electric field and bunching ofthe electrons takes place according to known laws. The bunched beam thenpasses the second gap and gives up high frequency energy to theoscillating field across this gap.

One of the difiiculties in the design of oscillators of the kindreferred to is due to the fact that for a system, comprising thetworesonant chambers and connecting electron path, of given shape,whilst the losses increase as ,f f being the frequency of oscillation,the electron beam area diminishes as F. These factors limit both thepower output and the highest frequency obtainable.

One object of the present invention is to eliminate this disadvantageand according to the invention the oscillating system is so shaped thatthe Wavelength of the oscillations generated thereby is independent ofat least one dimension of the system. This dimension is preferablysubstantially perpendicular to the direction of motion of the electronsin the beam. It is easy to show that, apart from a small correctionterm, the losses are proportional to f and. the beam area isproportional to f Hence whilst in the previous case the current densityin the just-oscillating condition is proportional to f, in the resonatoraccording to the invention it is still proportional to f.

In an ultra-high frequency oscillator according to the invention, it istherefore possible to vary said dimension without varying the wavelength of the generated oscillation, and at the same time to vary thepower output of the oscillator by increasing the electron beam area. Itis a further object of this invention to provide a constructional formof resonant chamber system which lends itself to the easy adjustment ofthe power output.

9 .It is a further object of this invention to pro vide a constructionalform of resonant chamber system which lends itself to mass productionmethods and in which component parts of standard sizes may be combinedtogether to produce easily and quickly a chamber system-in which atleast one dimension may be easily adjusted with a view to obtaining anincreased power output at a givenfrequency.

According to another aspect of the invention the method of constructingthe resonant chamber structure in or for an ultra. high frequencyelectron discharge device comprises stacking up a plurality of metallicsheets whose planes are parallel to the lines of high frequency currentflow and which have apertures corresponding to the desired cross-sectionor cross-sections of the resonant chamber or chambers and slotscorreponding to the necessary gaps.

According to another aspect of the invention, in an ultra-high-frequencyelectron discharge device of the velocity modulation type the resonantchamber structure is constituted .by a stack of plates.

According to another aspect of the invention in an ultra-high frequencyelectron discharge device of the velocity modulation type, the resonantchamber structure is built up from a plurality of like apertured plates.

The invention will be better understood from the following'descriptiontaken in conjunction with the accompanying drawings in which:

Figure 1 shows a perspective view of the resonant chamber systemaccording to the invention; a

Figure 2 shows in perspective view constructional form; 3

Figure 3 is a side view of the form shown in Figure 2; I t

Figure l is a side view of the system mounted in a support; f

Figure 5 is a sectional plan View of the con.- struction shown in Figure4;

Figure 6 isan exploded view of part of the construction shown in Figure2;

Figure 7 is a side view of another construction of resonator according.to the invention;

Figure 8 is a plan view of the construction shown in Figure 7, and

, Figure ,9 is an exploded view of part of the construction shown inFigures. '7 and 8.

Figuresloand 11 are two views at right angles of a complete deviceembodying the invention. Referring now .to Figure 1, four resonantchambers are shown ascylindrical bores in asolictmass of ':metal,ioninstance .of copper. The ibores are a preferred arranged in pairs,la, lb and 2a, 2b, one bore of each pair being on either side of anarrow channel 3 along which an electron beam is directed. Each resonantchamber or bore is provided with a longitudinal slit or opening asindicated at l8 and 19 which connects the chamber with the channel orbeam gap 3.

The electron beam producing means and the electron collecting electrodesare omitted from the drawing. In this form of construction, thedimension [3 of which the oscillation generated is independent is thelongitudinal length indicated by [3 in the drawing. This resonator isplaced in a tube with end plates placed at equal distances from theupper and lower surfaces.

In operation, the electrons first pass the gap I8, the modulating gap,when the beam is velocity modulated, absorbing a negligible amount ofenergy from the high frequency field across the gap. The electrons thentraverse the space between l8 and IS in which they are shielded from:the high frequency field and the beam is bunched according to knownlaws. The bunched beam then crosses the gap Hi, the working gap, andgives up energy to the high frequency field across the gap.

' The resonant circuits comprising the chambers are closely coupledwithout the introduction of any special coupling devices and oscillationof nearly the same amplitude and of the same or opposite phase in themodulating ciruits la,

lb," and the energy extracting circuits 2a, 2b can be maintained by thebeam. There are a series of discrete beam velocities for which a maximumoccurs in the high frequency energy transferred from the beam, giving aseries of possible operating voltages.

It will be observed that a resonator of the type described possesses theadvantage that there is no interruption or possible faulty connection inthe path of the high frequency currents where the intensity is high.

In the embodiment of the invention described the resonant wave lengthis, neglecting end effects, fixed only by the cross section of theresonant chamber which may be any other shape than circular.

The construction shown in Figure 1 is not easy to construct, owing tothe difliculty of lining up the cathode when the slot or beam gap 3along which the beam travels has a very small depth, I *5 (Fig. 1). Itis essential that'the depth of this beam gap be not too great, owing tothe reduced efliciency which would result from any large penetrationofhigh frequency field along the path of the beam. This is particularlyimportant if it is desired that the system should operate at a lowvoltage. At, for example, 400 volts, it is desirable that the beam gapdepth I5 should not exceed 0.015 of the operating wavelength. At 3 cm.wave-length this is only 0.045 cm.

Figures 2 to 6 show a form of construction of the embodiment shown inFigure 1 which overcomes this difiiculty and at the same time makes itpossible to use an appreciably increased current and makes manufacturequicker and easier. Figures 2 to 5 show the form of a resonator whichhas been successfully operated at 3.16, cm. wavelength. The depth of thebeam gap 3 is increased over that allowable in the structure shown inFigure 1 and the correspondingly increased penetration of theoscillatory field which would occur, is prevented by the introduction ofmetal strips 4 arrangedacross thegap andspaced'along the width 14(Figure4) of 'thebeam gap. 'If the width of the beam gap, is 0.2 cm.,the thickness of the metal strips is 0.40 mm., and these strips form agrid across the beam gap as is clearly seen at 4 in Figures 3 and 4. Thedirection of the beam is indicated by the arrows ll shown in Figure 5.The electron gun is shown diagrammatically at It and the collectingelectrode at H.

In order to enable the insertion of the strips 4 the resonator structureis compiled from thin metal sheets stacked one upon the other.

The exploded view of Figure 6 showing only three sheet elements of thestructure, indicates how the structure is built up from sections such as5, 6, 1 of metal sheet. For instance, sections 5 and I, which may be ofcopper but preferably of molybdenum, or other high heat resisting metalto obtain a greater loading than with copper, provide the metal strips 4shown in Figure 4. The section 6 which may be of copper or ofmolybdenum, for example, when temperature considerations must be takeninto account comprises two distinct similar parts showing a spacebetween them equal to the beam gap depth of Fig. 4. These sections ofmetal sheet may be readily punched out in large numbers and assembled toform a structure of any desired length according to the power which isdesired. When the sheets have been assembled, they are held in alignmentby means of a frame or tubular member 8 into which they may be slid, andare capped at top and bottom of the pile by means of thicker end plates,forexample of copper, 9, l0, as shown in Figure 4 so as to terminate thebeam gap width. Apertures [2 are provided in each sheet and cap for theinsertion of bolts or rivets for clamping the sheets together. The wholeof the stack or only the part relevant to the electron beam is insertedin an evacuated envelope. It will be seen that the advantage mentionedin relation to the structure shown in Figure 1, namely, that there areno interruptions in the high frequency circuit where the high frequencycurrent is high, is maintained in this construction shown in Figures 2to 6.

This mode of construction is also applicable to similar structures foroperating with longer wavelengths, for example, in the region of 5 to 40cm. or even longer, making it possible to use very much lower voltageswith higher currents to deliver a larger amount of power than theoscillators using resonators constructed from one solid mass as shown inFigure 1. Figures 7, 8 and 9 show another form of construction, in whichthe same references are used as in Figures 4, 5 and 6 to designate likeparts. It is not considered that any further description of thesefigures is necessary.

The electron discharge device shown in Figures 10 and 111s an ultra highfrequency oscillation generator adapted to feed electromagnetic wavesinto a wave guide by means of a rod antenna 24 secured in electricalcontact to the top plate 9 of the stack of plates forming the resonatingcavity system, at an antinodal point. The part embodying'the presentinvention is the stack of rectangular plates designated 20 and theassociated electron beam producing means. This stack 20 and the endmember 9 sandwich between them a mica plate 30 of annular formation anda metallic plate similarly apertured to the other plates, but of smallerexterior dimensions is inserted in the aperture in mica plate 30 so asto maintain the metallic and electrical continuity of the stack and topplate 9. A further mica plate 29 is provided at the bottom of the-stack20, and

between the mica plates 29 and 30 are mounted in position the electrodesfor producing the beam of'electrons. The cathode and control grid areshown at I6 and the anode at 3| with a collecting electrode I! behindthe anode. The electrode I1 is primarily of experimental value as anoscillation detector and the anode 3| has an aperture to allow some ofthe electrons to pass through to the collector electrode ll, thepresence of oscillations being shown in a circuit connected to H.

The plates of the stack are held together by bolts which pass throughapertures such as, l2 shown in Figures 2, 5 and 6. The Whole structureis mounted on the base of a U-shaped member 28 through which pass twobolts which are secured by means of nuts 21. Th member 28 is thensecured to two supporting pillars secured in the press of the glassenvelope 25.

For a fuller description of this device shown in Figures and 11reference may be made to the specification of co-pending application ofJ. H. Fremlin and C. H. Foulkes, Serial No. 476,465, filed February 19,1943, and now U. S. Patent No. 2,476,971.

Frequency variation can be obtained by the interposition of dielectricor conducting rods into the oscillatory circuit or by other known meanssuitable to tubes in which the oscillatory circuit is in an evacuatedbulb.

Whilst the resonant chambers have been shown as of circular crosssection, they may of course be of any desired shape, for example,rectangular or elliptical.

It will also be understood that the invention is not limited toresonators formed in a solid mass, but they may equally well be made upfrom bent ,metal sheet. It will also be understood that the method ofconstruction described is also applicable to single chamber systems, forexample as incorporated in an electron velocity modulated dischargedevice of the reflected beam type, or to systems having more than tworesonant chambers.

What is claimed is.

1. An ultra high frequency electron discharge device comprising a cavityresonator including a stack of like apertured conducting plates, meansforming an electron path through said resonator parallel to the planesof said plates and transversely of the depth of said stack, and certainof said conducting plates being slotted for coupling the cavities ofsaid resonator to the electron beam.

2. An utra high frequency electron discharge device comprising a cavityresonator block having cavities of uniform cross sections along theirrespective linear longitudinal axes and gaps connecting said cavitieswith a linear beam gap in said block, said block comprising a stack ofthin metal stampings having apertures corresponding to the crosssections of the resonant cavities and having slots corresponding to saidgaps, and means at one end of said beam gap for producing a beam ofelectrons and for directing said beam along said beam gap.

3. An ultra high frequency electron discharge device comprising aplurality of stacked conducting plates, each having a plurality ofapertures in alignment and slots connecting said apertures to an outsideedge of said plates at spaced points, said plates being stacked with thecorresponding apertures of said plates in alignment and thecorresponding slots in alignment, and means aligned with said points forproducing a beam of electrons along a path parallel with saidedge 6 andfor directing said beam past the slots of a plate in succession.

4. An ultra high frequency electron discharge device according to claim3, comprising further 5 conducting plates of high heat resistance havinglike apertures to those in the first mentioned plates, said furtherplates being interleaved between said first mentioned plates in thestack with their apertures in alignment with the apertures in said firstmentioned plates, said further plates having portions extending intosaid path of said electron beam.

5. An ultra high frequency electron discharge device comprising a pairof stacks of conducting plates each plate having a plurality ofapertures and slots connecting said apertures to an outside edge of saidplate, the plates in each stack being stacked with correspondingapertures of said plates in alignment and the corresponding slots inalignment, means retaining the two stacks in fixed relative positionswith corresponding slots {directly opposite each other and with a spacebetween said stacks forming a beam gap, and means-aligned with said beamgap for producing a beam of electrons and for directing said beam alongsaid beam gap plates.

6. An ultra high frequency electron discharge device according to claim5 comprising further conducting plates of high heat resistance havingapertures corresponding to those in the first mentioned conductingplates, and having slots connecting a pair of apertures in said furtherconducting plates corresponding to a pair of apertures on opposite sidesof said beam gap and immediately opposite each other, said furtherplates being interleaved between the conducting plates of the said twostacks with their apertures in alignment with corresponding apertures insaid stacks and said further plates having portions extending acrosssaid beam gap.

7. An ultra high frequency electron discharge device comprising twostacks of like apertured conducting plates with a beam gap therebetweenfor the passage of an electron beam, the apertures in said platesforming cavities of uniform cross section along the depths of the stacksand said plates having longitudinal slots connecting the said cavitieswith the beam gap, further conducting plates of high heat resistanceinterleaved with the plates of said two stacks and extending across saidbeam gap, said further plates having apertures corresponding ,to saidcavities and having slots connecting pairs of apertures on oppositesides of said beam gap.

55 8. An ultra high frequency electron discharge device according toclaim 7 further comprising Q; thicker plates at the top and bottom ofsaid two stacks of plates and like apertured to said further conductingplates defining a greater depth of said cavities.

9. An ultra high frequency electron discharge device comprising alaminated resonator block, .the laminae of the block comprising thinmetal plates having at least one round hole and a com- 65 municatingnarrow slot formed therein, the

laminae being stacked with the holes and slots in registry to define acylindrical bore and an elongated narrow cavity extending longitudinallyof the block. 70 10. An electron discharge device comprising a laminatedresonator block, the laminae of the resonator block comprising aplurality of thin sheet metal discs, the discs each having a round,hole, and a communicating narrow slot, the holes 'l' 'izand slots beingin registry in the stack of discs defining a cylindrical bore and anelongated narrow cavity extending longitudinally of the block, saidnarrow cavity being extended to open through a wall surface of saidblock outside of said bore in the form of an elongated narrow slot insaid wall surface, and means forming an electron path transverselyacross said narrow slot substantially throughout the length thereof andin a direction substantially parallel with the planes of said discs.

11. An electron discharge device comprising a source of electrons, alaminated block adjacent said source of electrons, said block comprisinga series of stacked laminae, each lamina having a space in whichelectrons may flow from said source, and a space forming a cavityresonator connected to said first space.

12. An electron discharge device comprising a laminated resonator block,the laminae of the resonator block comprising a plurality of thin sheetmetal discs, the discs each having a round hole, and a communicatingnarrow slot, the holes and slots being in registry in the stack of discsdefining a cylindrical bore and an elongated narrow cavity extendinglongitudinally of the block, said narrow cavity being extended to openthrough a wallsurface of said block outside of said bore in the form ofan elongated narrow slot in said wall surface, an electron emittingelement positioned between the end planes of said resonator block, andmeans including anode JOHN BEAVER. FREMLIN. JOHN FOSTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 342,553 Westinghouse May 25, 18861,661,830 Hull Mar. 6, 1928 1,684,947 Daumann Sept. 18, 1928 2,043,733Brasch et al June 9, 1936 2,044,413 Weyrlch June 16, 1936 2,063,342Samuel Dec. 8, 1936 2,157,952 Dallenbach May 9, 1939 2,193,600Mouromtseil et al. Mar. 12, 1940 2,202,380 Hollrnann May 28, 19402,209,923 Kilgore July 30, 1940 2,270,777 Von Baeyer Jan. 20, 19422,289,984 Mouromtsefi et a1. July 14, 1942 FOREIGN PATENTS NumberCountry Date 215,600 Switzerland Oct. 16, 1941

